Finding a vented cap is pretty impossible I think. I couldn't find any "new" gas caps at all for this car. I checked the service manuals/parts manuals, and no the cap doesn't have a vent.

Drilling that hole might actually be the best route, but I'll look and see if I can get a new cap first.

On my Mazda there is a breather pipe connected to the filler neck that goes to the tank. There are what I think ventilation pipes on top of the tank as well. Im not sure sure how they all connect together, however the Subaru must have something similar aside from a fuel line and fuel return line. I doubt the problem has anything to do with the fuel pump.

Door rubbers can be a pain when new, I adjusted my doors and kept them shut for a month. They seem to have bedded in now. Some people rub vaseline into them to help soften them up, I didnt need to do that with mine. If you search the net it seems a common complaint. Sometimes the reproduction seal is simply the wrong shape, and hardness or both. If they don't breakin after a month they probably never will.

Everyone with a project like this can get problems te keep it up. Look back on what you have done, a huge effort with outstanding results. The work is of immaculate quality, it would be a pitty to give that away. I would say stall the car in a good place and go on with it as energy level is back again